Work to replace 120 corroding anchor bolts in Canberra's Scrivener Dam will begin next week.

The anchor bolts ensure the dam's five flap gates remain secured to the concrete wall.

The flap gates are lowered during flood events to regulate the level of Lake Burley Griffin.

The National Capital Authority's (NCA) Gary Rake says a safety audit in 2011 found problems with the bolts.

"We've found that we can design a new system, that will use half as many bolts, that we can put in place faster and within budget and it will give us a fresh design life of 100 years," he said.

"We're not even fixing this to be good for another 50 years, which is the problem we have inherited, we're making this good for at least another 100 years."

Mr Rake says the NCA was sure the corroding bolts would hold the flaps, but with little margin for error.

"Certainly if they failed without warning there would be a real risk for people who were in the river downstream of the dam or people who were on the lake upstream," he said.

"We took action immediately and that was to lower the level of the lake by half a metre and put us back in a safe position so that we could take the time necessary to understand the problem, design the solution, set about getting the approvals and in a couple of weeks time get on with the work."

Mr Rake says there will be minimal impact on road users during the works, which are expected to be completed by March 2014.